The present invention provides an arrangement which is intended to be used in an antenna array for transmitting and receiving at at least one frequency in at least two polarizations preferably in the microwave range.
The arrangement comprises a plate with antenna elements, where the antenna elements are fed by waveguides in an underlying plate which is part of a feeding structure. The specific construction according to the invention of the feeding structure provides a possibility of placing rows of antenna elements intended for a first polarization between rows of antenna elements intended for a second polarization whilst keeping the grating lobes of the antenna at a low level.
1. Prior Art
When transmitting electromagnetic signals in a system in, for example, the microwave range, it is very desirable that the antennas which are used in the system should be as small and compact as possible and, at the same time, provide a system in which they are included with the highest possible transmission capacity.
One way of constructing an antenna which provides a system which has a high transmission capacity is to make the antenna dual-polarized, in other words, to give one and the same antenna the capability of operating on two different polarizations.
A dual-polarized antenna can increase the transmission capacity in the system by transmitting in a different polarization. Furthermore, a dual-polarized antenna can, for example, transmit and receive in different polarizations which reduces the requirement for filters in the system. Furthermore, one possibility which is created with the aid of a dual-polarized antenna is to use so-called polarization diversity, in other words, to transmit/receive the same information in both polarizations and to utilize the signal which happens to be the strongest, or, alternatively, to combine the two signals to increase the signal level.
A dual-polarized antenna is normally intended for use at one and the same frequency in two different polarizations but it is quite possible to have different frequencies in the different polarizations.
There is a number of different known techniques for making dual-polarized systems or antennas. One example of such a known technique is quite simply to arrange two antennas with different polarization next to each other. This provides a relatively good operation but is a space-consuming solution. Another known technique for dual-polarized antennas is to use reflector antennas with feeders which operate for the different polarizations. However, reflector antennas, too, are a space-consuming solution.
Among other examples of known techniques for dual-polarized antennas, antennas can be named which are constructed in microstrip technology. However, known dual-polarized antennas in microstrip technology give relatively high losses.
One concern in the manufacture of dual-polarized so-called antenna arrays is to avoid the possibility of so-called grating lobes. Grating lobes arise, for example, if the antenna elements in the antenna array which are intended for the same polarization and the same frequency are placed too far from each other which can happen if the antenna elements intended for the first polarization of the antenna are placed between antenna elements intended for the second polarization of the antenna.
2. Description of the Invention
The problem which is solved by the present invention is thus to be able to make a dual-polarized antenna array which is small and compact, inexpensive to produce and has small or negligible grating lobes.
This problem is solved with the aid of an arrangement for use in an antenna array for transmitting and receiving at at least one frequency in at least one first and one second polarization, which comprises at least two antenna elements, where each antenna element is intended for one of the two polarizations, with the antenna elements being arranged in a feeding structure which conducts electrical signals to and from the antenna elements. The feeding structure comprises a number of waveguides dimensioned for the said at least one frequency, and different waveguides are used for feeding antenna elements intended for different polarization. According to the invention, the waveguides are completely or partially filled with a material, the dielectric constant of which is higher than that of air.
In a preferred embodiment, the waveguides in the feeding structure are essentially rectangular with a longitudinal direction and a transverse direction, and are arranged in parallel rows with one or more waveguides in each row. One of two adjacent rows of waveguides is suitably used for the first polarization and the second row is used for the second polarization. The antenna elements are suitably also arranged in rows in the same direction as the rows of waveguides, with one or more antenna elements for each waveguide.
According to the invention, the waveguides can be constructed with dimensions which allow one row of waveguides intended for the one polarization to be placed between two rows of waveguides intended for the second polarization at the same time as the distance between two rows of waveguides intended for the same polarization is such that the level of the grating lobes is low or negligible. Furthermore, according to the invention, the antenna element s in one and the same row can be placed closer to one another than otherwise, which also contributes to the avoidance of grating lobes.
The antenna elements can be suitably arranged in a first separate plate which has its major extension in a first and a second plane of extension. The first plate is arranged on the feeding structure which also includes at least one second separate plate which has its major extension in a first and a second plane of extension. In the second plate, a number of continuous recesses are arranged which are constructed to function as waveguides at the said at least one frequency. This plate structure makes the arrangement simple and inexpensive to produce.
The invention thus provides a capability of creating a compact single-frequency or multi-frequency dual-polarized antenna array which has small or negligible grating lobes. An antenna array with an arrangement according to the invention can also be produced at low cost.
The invention also provides the capability of constructing an arrangement for use in an antenna array for transmitting and receiving at at least two frequencies in one polarization, comprising at least two antenna elements, where each antenna element is intended for one of the at least two frequencies, the antenna elements being arranged on a feeding structure which conducts electrical signals to and from the antenna elements, and where the feeding structure comprises a number of waveguides dimensioned for the said at least two frequencies, whereby different waveguides are used for feeding the antenna elements intended for different frequencies, and the waveguides are completely or partially filled with a material, the dielectric constant of which is higher than that of air, whereby an alternative antenna array with small or negligible grating lobes can be obtained.